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CN-121990713-A - Method, equipment and application for preparing high-purity calcium fluoride from concentrated acid wastewater of photovoltaic cell in situ

CN121990713ACN 121990713 ACN121990713 ACN 121990713ACN-121990713-A

Abstract

The invention relates to the field of wastewater treatment, in particular to a method, equipment and application for preparing high-purity calcium fluoride from concentrated acid wastewater of photovoltaic cells in situ. The method comprises the steps of (S01) preparing a compound calcium salt solution from calcium hydroxide and calcium hydroxychloride, pumping the compound calcium salt solution into concentrated acid wastewater to react to generate calcium fluoride particles, (S02) adding a citric acid solution into the mixed solution after the reaction in the step (S01), (S03) applying micro-current to the mixed solution after the treatment in the step (S02) to change the surface charge property of the calcium fluoride particles, (S04) adding a flocculating agent into the mixed solution after the treatment in the step (S03) to flocculate and settle the calcium fluoride particles to obtain calcium fluoride flocculated sludge, and (S05) carrying out filter pressing dehydration on the calcium fluoride flocculated sludge obtained in the step (S04) and drying and calcining a filter cake after dehydration. The invention adopts calcium salt reaction, citric acid regulation, micro-current modification, flocculation separation, dehydration and calcination to be carried out continuously, and no extra acidification and impurity removal steps are needed.

Inventors

  • TAO JIE
  • XIE CHAO
  • SONG WEI

Assignees

  • 安徽科博瑞环境科技有限公司

Dates

Publication Date
20260508
Application Date
20260210

Claims (10)

  1. 1. The method for preparing the high-purity calcium fluoride in situ from the concentrated acid wastewater of the photovoltaic cell is characterized by comprising the following steps of, (S01) pumping a compound calcium salt solution prepared from calcium hydroxide and calcium hydroxychloride into concentrated acid wastewater to react to generate calcium fluoride particles; (S02) adding citric acid solution into the mixed solution after the reaction in the step (S01); (S03) applying a microcurrent to the mixture after the treatment of step (S02) to change the surface charge properties of the calcium fluoride particles; (S04) adding a flocculating agent into the mixed liquor treated in the step (S03) to flocculate and settle calcium fluoride particles, so as to obtain calcium fluoride flocculated sludge; (S05) carrying out filter pressing dehydration on the calcium fluoride flocculation sludge obtained in the step (S04), and drying and calcining a dehydrated filter cake to obtain the high-purity calcium fluoride.
  2. 2. The method of claim 1, wherein the concentration of the compound calcium salt solution in the step (S01) is 5% -15%, the concentration of the compound calcium salt solution is 8% -12%, the compound calcium salt solution in the step (S01) is continuously pumped into a concentrated acid reaction tank by a metering pump, the reaction tank is three sections and is provided with reflux, the reaction time of the last section of the reaction tank is 30-60 min, the total reaction time is 60-90 min, and the delivery of the compound calcium salt solution by the metering pump is stopped when the pH value of the effluent of the reaction tank is stabilized at 7.5-8.5.
  3. 3. The method of claim 1, wherein the concentration of the citric acid solution in the step (S02) is 1-5%, the metering pump is stopped when the pH of the reacted mixed solution is adjusted back to 6.5-7.0 by the citric acid solution, the stirring time in the adjusting back process is 10-20 min, the current density in the step (S03) is 5-10 mA/cm < 2 >, and the microcurrent acting time is 1-2 h.
  4. 4. The method of claim 1, wherein the flocculant in the step (S04) is polyaluminum chloride and polyacrylamide, the concentration of polyaluminum chloride is 2-10%, the adding amount is 1-3% of the amount of concentrated acid water, the reaction time is kept for 30-60 min under the condition that the pH value is 5.5-6.5, the polyacrylamide adopts a cationic flocculant, one of the ionic degrees of 50, 60, 70 and 80 is selected, the polyacrylamide adopts a cationic flocculant and is respectively conveyed from a storage tank to a flocculation reaction tank through a third metering pump, mixing is achieved through stirring, the concentration of the polyacrylamide is 2-5%, the adding amount is 15-30% of the amount of concentrated acid water, and the stirring time is 30-60 min.
  5. 5. The method of claim 1, wherein the step (S05) is characterized in that the calcium fluoride sludge is obtained through plate-and-frame filter pressing, the water content of the calcium fluoride sludge after the plate-and-frame filter pressing is 40-50%, the water content of the calcium fluoride sludge after the plate-and-frame filter pressing is 45%, and the drying and calcining temperature in the step (S05) is 100-300 ℃ and the time is 12-24 hours.
  6. 6. The equipment for preparing the high-purity calcium fluoride in situ from the concentrated acid wastewater of the photovoltaic cell is characterized by comprising, The preparation tank system is used for conveying calcium hydroxide and calcium hydroxide compound calcium salt solution to the reaction tank system, and the reaction tank system is used for conveying mixed solution after the reaction to the flocculation system; The configuration tank system comprises a configuration tank (100), a tank cover (101) is arranged at the top of the configuration tank (100), and two quantitative tanks (200) for respectively adding calcium hydroxide powder and calcium hydroxychloride are arranged on the tank cover (101) in parallel; A first stirring paddle (103) driven by a first motor (102) is arranged in a configuration tank (100) in the configuration tank system, a large gear (104) is connected to a central shaft of the first stirring paddle (103), small gears (105) rotationally connected to a tank cover (101) are symmetrically meshed with two sides of the large gear (104), a gear shell (106) is connected below the tank cover (101), the large gear (104) and the small gears (105) are positioned in the gear shell (106), and a dispersing blade (107) is connected to the central shaft of the small gears (105); The central shaft of pinion (105) in the configuration tank system is also connected with a fan blade (109), the fan blade (109) is positioned in an air draft shell (108), the air draft shell (108) is arranged below the gear shell (106), one side of the air draft shell is provided with an air suction port (1081), an air outlet of the air draft shell (108) is connected with a blowing pipe (110), and the other ends of the blowing pipes (110) are respectively communicated with two quantitative tanks (200).
  7. 7. The device for preparing high-purity calcium fluoride from concentrated acid waste water of photovoltaic cells in situ according to claim 6, wherein an outlet end of the blowing pipe (110) is connected with a diffusion shell (111), a shaft body (202) driven by a second motor (201) is arranged in the quantifying tank (200), a straight spiral blade (203) and a conical spiral blade (204) are arranged on the shaft body (202), a bulk cargo plate (205) is arranged above the conical spiral blade (204) in the quantifying tank (200), a scraping plate (206) is connected to one side below the shaft body (202) in a sliding manner, a first spring (207) is connected between the scraping plate (206) and the shaft body (202), the first spring (207) drives the scraping plate (206) to be always in contact with the inner wall of the quantifying tank (200), a second spring (210) is sleeved on the shaft body (202), a conical block (209) is connected to the sliding rod (208), and the other end of the second spring block (210) is connected with the sliding rod (209).
  8. 8. The apparatus for in-situ preparation of high purity calcium fluoride from concentrated acid waste water of photovoltaic cell according to claim 6, wherein the reaction tank system comprises a first reaction tank (300), the first reaction tank (300) is communicated with a second reaction tank (303) through a first overflow pipe (302), the second reaction tank (303) is communicated with a third reaction tank (305) through a second overflow pipe (304), the configuration tank (100) is communicated with the first reaction tank (300) through a first metering pump (301), the effluent of the third reaction tank (305) is discharged through a third overflow pipe (306), mechanical valves are arranged in the first overflow pipe (302), the second overflow pipe (304) and the third overflow pipe (306), each mechanical valve comprises a sealing cover (309), one end of each sealing cover (309) is hinged to the inner wall of the overflow pipe, a push rod (307) is movably connected above each sealing cover, the upper end of each push rod (307) extends upwards through the overflow pipe and is sleeved with a lock sleeve (308), and the lock sleeve (308) is fixedly connected to the reaction tank.
  9. 9. The device for preparing high-purity calcium fluoride from concentrated acid wastewater of photovoltaic cells in situ according to claim 8, wherein the first-stage reaction tank (300), the second-stage reaction tank (303) and the third-stage reaction tank (305) are respectively provided with a third motor (400), an output shaft of the third motor (400) is connected with a stirring shaft (401), a spline housing (402) is connected below the stirring shaft (401), a rotary table (403) is fixedly connected below the spline housing (402), stirring blades (404) are arranged on the rotary table (403), a hollow shaft (405) is fixedly connected below the rotary table (403), the hollow shaft (405) is rotationally connected with the bottom of the reaction tank, a screw (406) is movably connected in the hollow shaft (405), the screw (406) is in threaded connection with the stirring shaft (401), a third spring (407) and a sliding sleeve (408) are sleeved on the stirring shaft (401), one end of the third spring (407) is connected with the spline housing (402), and the other end of the third spring (407) is connected with the sliding sleeve (408).
  10. 10. The device for preparing high-purity calcium fluoride from concentrated acid wastewater of a photovoltaic cell in situ according to claim 8, wherein the flocculation system comprises a flocculation reaction tank (500), the three-stage reaction tank (305) is communicated with the flocculation reaction tank (500) through a third overflow pipe (306), a cavity is formed in the bottom of the flocculation reaction tank (500), a battery interface (501) is formed in one side of the flocculation reaction tank, an electrode plate (502) is inserted into the cavity through the battery interface (501), the electrode plate (502) is sealed with the battery interface (501) through a sealing ring and a threaded connection, a water outlet groove (503) is communicated with the cavity at the bottom of the flocculation reaction tank (500), a water outlet pipe is connected to an outlet of the water outlet groove, a valve (504) is arranged on the water pipe, two air pipes (505) are respectively communicated with the water outlet groove (503) through two side walls of the flocculation reaction tank (500), and the other ends of the two air pipes (505) are communicated to a tee joint (506).

Description

Method, equipment and application for preparing high-purity calcium fluoride from concentrated acid wastewater of photovoltaic cell in situ Technical Field The invention relates to the field of wastewater treatment, in particular to a method, equipment and application for preparing high-purity calcium fluoride from concentrated acid wastewater of photovoltaic cells in situ. Background The photovoltaic cell industry is one of the strategic novel industries which are preferentially developed in China, and the photovoltaic cell industry is rapidly developed in recent years. The waste water produced by etching monocrystalline silicon and polycrystalline silicon by hydrofluoric acid has obvious water quality difference. Including high fluorine concentrated acid wastewater, dilute acid wastewater, silane wastewater and concentrated alkali wool making wastewater. Because the pollutants brought by various production process sections are different, the impurities are more and are difficult to remove partially after calcium precipitation. The phosphorus diffusion section is provided with phosphorus oxychloride and phosphorus pentoxide, the surface of silicon is etched by concentrated alkaline water in the texturing process to bring high-concentration silicate, and in order to adjust the pH value of the system, sulfuric acid is added into a sedimentation tank to generate calcium sulfate impurities, so that the purity of calcium fluoride sludge is affected. The high-concentration fluorine is removed mainly by adopting calcium oxide, calcium hydroxide and calcium chloride to precipitate fluorine ions, so that calcium fluoride sludge is generated. At present, the recycling of the calcium fluoride sludge is to make bricks after treatment or prepare chemical additives, for example, the calcium fluoride sludge is used as a stabilizer for ceramic calcination, and the calcium fluoride sludge is used as a cosolvent for stripping and melting, and replaces river sand in concrete production. The added value is low, so that the fluorine resource waste is caused, and therefore, a new calcium fluoride sludge recycling path is sought. At present, the domestic photovoltaic enterprises adopt a brick making mode after calcination due to the defects of more impurities, low purity of calcium fluoride and the like, and the added value is very low. Patent document with publication number of CN108191118A discloses a method for recovering fluoride ions in wastewater, wherein fluoride ions in the wastewater are discharged up to standard through resin adsorption, resin desorption liquid is treated by adopting a process combining a diffusion dialysis technology and a chemical precipitation method, and high-fluoride wastewater in diffusion dialysis effluent is separated and recovered in a precipitation form by adopting the chemical precipitation method, but calcium fluoride sludge with high yield cannot be obtained in the method. The patent document with the publication number of CN110078109A discloses a method for preparing a high-purity calcium fluoride product from acidic fluorine-containing wastewater, which utilizes multistage calcium carbonate to treat high-fluorine concentrated acid solution to prepare high-purity calcium fluoride, wherein the calcium fluoride can be adsorbed on the surface of the calcium carbonate, the utilization efficiency is reduced, a large number of bubbles can be generated in the reaction, and potential safety hazards exist in practical application. The patent document with the publication number of CN110790295B discloses a method for preparing high-purity calcium fluoride from calcium fluoride sludge, wherein the method is used for removing impurities by acidification to remove carbonate and removing silicate under alkaline water, but the method is complex in operation, can generate a large amount of fluorine-containing cleaning wastewater, generates secondary pollution and has low practical application possibility. Therefore, if the calcium fluoride sludge with higher purity is obtained, the production wastewater is treated in a classified manner. Because the concentrated acid wastewater is mainly hydrofluoric acid, the concentration of fluoride ions is high, and the independent treatment of the concentrated acid wastewater is the most practical direction for preparing high-purity calcium fluoride. However, calcium fluoride has smaller crystals, slow deposition rate, difficult separation and low purity. In addition, as concentrated acid water is used alone, which causes acid-base imbalance of the whole system, more acid needs to be added, which also causes the increase of operation cost and the increase of sulfate ions in effluent. Therefore, the problems of low purity of the calcium fluoride product, difficult source inhibition of impurities, tiny calcium fluoride crystal, low solid-liquid separation efficiency, low yield, high cost, potential safety hazard or poor practicability exist in the prior art. Disclosur